The present invention relates to web handling, and more particularly relates to web transport apparatus for feeding webs through web treatment apparatus.
In numerous industrial applications, flat materials such as paper, film, foil and the like are handled in semicontinuous web form. Such materials are often processed by drawing each web through the active zone of a treatment device and operating the treatment device while the web is moving through it.
Web transport apparatus is used to draw the webs through the treatment device. The transport apparatus normally includes a payout stand, a takeup stand and support structure defining a transport path which extends from the payout stand to the takeup stand. The transport apparatus is juxtaposed with the treatment device so that the transport path extends through the active zone of the treatment device. A coil containing each web is loaded into the payout stand and the leading end of the web is threaded along the transport path to the takeup stand. The web is then drawn through the active zone of the treatment device by winding it onto a coil at the takeup stand while unwinding it from the coil at the payout stand.
After each web has been completely fed through the apparatus in this manner, it is removed from the apparatus and a new web is loaded and threaded. With the web transport apparatus of the prior art, the treatment device has been idle during each such unloading and reloading cycle. Certain types of web treatment devices can process webs at extremely high speeds. The web transport apparatus associated with such devices must be reloaded frequently so that the productive capacity of such treatment devices is diminished.
For example, a laser beam treatment device can perforate cigarette tipping paper drawn through it at a linear speed of up to 7,000 feet per minute. Even if the paper is supplied in webs of the maximum practicable length, the transport apparatus used with such a treatment device must be reloaded after only about 2 to 3 minutes of operation. If each such reloading cycle takes only one minute, from 25 to 33 percent of the productive capacity of the treatment device will be lost.